[IndVars] Avoid repeated hash lookups (NFC) (#107513)

Author: kazutakahirata

llvm/lib/Transforms/Utils/SimplifyIndVar.cpp

@@ -1103,10 +1103,8 @@ class WidenIV {
 
   void updatePostIncRangeInfo(Value *Def, Instruction *UseI, ConstantRange R) {
     DefUserPair Key(Def, UseI);
-    auto It = PostIncRangeInfos.find(Key);
-    if (It == PostIncRangeInfos.end())
-      PostIncRangeInfos.insert({Key, R});
-    else
+    auto [It, Inserted] = PostIncRangeInfos.try_emplace(Key, R);
+    if (!Inserted)
       It->second = R.intersectWith(It->second);
   }